Communications cables with sealed metallic moisture barriers

ABSTRACT

Successive portions of an aluminum tape having one major surface thereof coated with an adhesive copolymer across the entire transverse width thereof and the other major surface precoated with a stripe of adhesive material along an edge portion are folded longitudinally about successive sections of a cable core which are being advanced along a predetermined path to form an overlapped seam so that the adhesive copolymer on an edge portion of the one major surface of the tape overlaps the stripe. Subsequently, the adhesive materials on the major surfaces along the overlapped seam develop an adhesive bond by the application of heat and pressure prior to or during the extrusion of a plastic jacket over the tape. The adhesive material on the other, now inwardly facing, major surface is substantially restricted in location and is adhesively bonded to the portion of the inwardly facing major surface of the tape which forms the overlapped seam with a portion of the one, now outwardly facing, major surface. The remaining portion of the inwardly facing major surface of the aluminum tape is bare and facilitates grounding the cable at a splice location.

United States Patent D m et 9 11 .21 Nov. 21j,197 2 [54] COMMUNICATIONS CABLES WITH 338,437 6/1958 Froemrning etal ..174/ l 1Q SEALED METALLIC MOISTURE M BARRIERS r I a I j j 3,424,631 1/1969 Peacock..'......'.. ...174/ 120 R'X i 3,032,604 7 5/1962 Timmons ..'...'.174/l 15 [72] .lnventors: Matthew R. Delnbiak, Clifton, N.J.; 3,409,734 11/1968 9 De Vine et al... ...l74/ 113 R George H, Webster, Tlmonium, Md; 3,471,350 10/1969. OBerry et al...174/l17 A UX [731 Assignees? western p i' 'f Primary Examiner-Remard A. Gilheany New York by saldrDemblak Assistant Examiner-A. T. Grimley T r m' g g gfg g g i gf Attorney-W. M. Kain, R. smaller and Don P. Bush [221 Filed: March 17,1971 1571 v I ABSTRACT [211 App], 125,3 2 {Successive portions of an aluminum tape having one ma or surface thereof coated with an adhesive Related US. Application Data copolymer across the entire transverse width thereof {and the other major'surfa'ce precoated with a stripe of a a gg fig'g' g .adhesive material along an edge portion are folded arc a an longitudinally about successive sections of a cable jco're which are being advanced along a predetermined"- [52] US. Cl ..174/107, 174/36, 174/ 110 PM Path to fox-man overlapped seam so that the adhesive Int. Cli poly on an e-dg portion the one major guy. Field fl /3 102 102 D, 1 face of the tape overlaps the stripe. Subsequently, the 3 1 1 10 adhesive materials on the major surfaces along the v I QSR overlapped seam develop an adhesive bond by cheapplication of heat and pressure prior to or during the [56] References Cited extrusion of a plastic jacket over the tape. The adhesive material on the other, now inwardly facing, major UNITED STATES PATENTS surface is substantially restricted in location and is adv3,504,102 3/1970 POIiZZaHO ....174/107 hesively bonded to the Portion of the inwardly facing 3,379,321 4/1968 Garner .......174/36 maim shrface tape which frms the PP 3,424,631 1/1969 Peacock ..174/ R a the twamly facing" 3,233,036 2/1966 Jachirnowicz ..174/107 f The emammg h inwa'dly 3 274 329 9/1966 Timmons 174/115 x facing major surface of the aluminum tape is bare and 9 9 v a n I u I I I a s 6 a n s 1 I e 3,574,016 4/1971 Wahlberg ..174/ 107 x 2 h hi9 asphc? 92? 3 1 0 6 i 7 Claims, 5 Drawing Figu res COMMUNICATIONS CABLES WITH SEALED METALLIC v MOISTURE BARRIERS CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates tocornmunications cables with sealed metallic moisture barriers and the methods of making same, and more particularly, to an electrical cable in which successive portions of a metallic tape are precoated on at least part of one major surface with an adhesive copolymer material and along an edge por tion on the other major surface with a stripe of adhesive material and then wrapped longitudinally about a core to form an overlapped seam with an adhesive bond occurring between the adhesive materials on the overlapped portions of the tape.

2. Technical Considerations and the Prior Art In the cable industry, it is well known thatchanges in the ambient conditions lead to differences in vapor pressure between the inside and the outside of a plastic cable sheath which generally operates to diffuse moisture in a unidirectional manner from the outside of I the cable to the inside of the cable. This eventually will lead to an undesirably high moisture level inside the cable, especially if a polyethylene jacket is the only barrier to the ingress of the moisture and, high moisture levels inside a cable sheath may have a detrimental effect on the transmission characteristics of the cable.

Polyethylene which is used in the jacketing of a ca ble, prevents the passage of water only on a microscopic scale. Where cables are in use for periods of 20 to 40 years and where the conductors within the cables are sensitive to moisture vapor or liquid, it becomes necessary to consider methods of preventing the ingress of moisture into the cable not only on a microscopic but also on a molecular level.

A metallic barrier which is wrapped around a cable core is an effective barrier against diffusion of moisture into the cable core. Telephone cable of this construction is referred to in the art as Alpeth cable and is described more fully in the F. W. Horn and R. B. Ramsey paper Bell System Cable Sheath Problems and Designs in A.I.E.E. Proceedings 1951, Volume 70. Since most communications require an electrically conductive metallic shield to protect against external electrical signals, it is usually desirable to incorporate the shielding function with the moisture barrier function in one layer of metal. A metallic strip may be corrugated transversely prior to being folded about the cable core in order to give greater flexibility to the cable and to permit bending of the completed cable without wrinkling or rupture of the shielding strip.

The barrier may be made from a single strip of metal, such as aluminum, in the form of a tape, which is wrapped longitudinally about the cable to overlap the edge portions. After the metallic tape of, say aluminum, is folded about the cable core to form a tube, an outer jacket of polyethylene is extruded over the tube. As the polyethylene cools, the polyethylene material contracts. The cooling proceeds from the I outer surface of the jacket inwardly with the shrinkage forcing the polyethylene into close engagement with the surface of the longitudinally folded tape and slides the overlapping edge portions of the metallic tape rela- .tive to each other to partially collapse the shield. The relative sliding movement of the overlapping edge portions is stopped when the tubular shield is supported against the cable core. During this shrinkage, the outer overlapping edge of the folded tape presses outwardly into the plastic jacket, thereupon reducing the efiective jacket thickness radially outward from the tape edge.

The slippage along the seam may be eliminated and the efiectiveness of the strip as a moisture barrier or shield enhanced substantially if the seam between the overlapping edges is sealed. More particularly, a seal is most effective in which a metal-to-metal bond of the overlapping edge portions is accomplished, for example, by welding or soldering. Generally though, the materials which are used in the cable core are temperature-sensitive and easily damaged if overheated. These characteristics render the use of welding, as a sealing technique, impractical because of the high temperature involved in most ordinary welding processes. Moreover, the aluminum, because of its highly reactive nature, generally maintains an oxide film which vitally precludes continuous soldering as a joining technique in situations such as manufacturing of a cable sheath. Therefore, other methods have been devised for sealing the overlappingedges of the seam of the aluminum, longitudinally wrapped, shield.

In order to improve the corrosion resistance of the barrier or shield and eliminate the slippage along the overlapping seam, a special adhesive copolymer consisting essentially of a polyethylene in form with attached carboxyl groups may be applied to both sides of the metallic tape to form a shielding layer. The adhesive copolymer which is an ethylene acid copolymer or more particularly, an ethylene acrylic acid copolymer, is applied in the form of a flexible protective film and has high electrical resistivity, high resistance to chemicals and moisture, and especially good adhesion to the aluminum to withstand both manufacturing processes, such as corrugating and longitudinal folding, and to prevent delaminations in corrosive environments. The application of adhesive copolymers in laminates is discussed by B. Wargotz in an article Environmental Stability of Ethylene-Acrylic Acid Adhesive Copolymers Bonded to Metal Substrates published in Vol. 12 of the Journal of Applied Polymer Science, pages 1873-1888 (1968).- Adhesive copolymers such as these develop a firm bond between the metallic strip and the outer polyethylene jacket.

Adhesively sealed metallic moisture barriers may be manufactured without resort to an'overlapped seam. Metal tapes, for example, have been formed into finned configurations wherein the two edge portions of a longitudinally applied tape are oriented radially of the cable core with the polymer coatings on the inner surfaces of each of these edge portions being in contact. The two edge portions are then heated and pressed to form a bond between the two copolymer coatings. The projecting sealed fin is then folded down to lie substantially parallel to the main portion of the formed tape. The sealing of the fin is sometimes accomplished by the heat of a polymeric jacket extruded over the metal tape rather than in a separate sealing operation.

The use of this finned seam system results in at least three thicknesses of materials along some part of the periphery of the metal tape and these multiple thicknesses of material add to the non-unifomiity in the thickness of a polymeric jacket applied over the metal tape. The forming and sealing of the tin type seam is much more difficult than forming an overlap seam.

A metallic, for example, aluminum tape, may be precoated on both major surfaces with the adhesive copolymer, across the entire width thereof, after which the precoated tape is folded longitudinally about the cable core. When a polyethylene jacket is applied over the core and metallic shielding layer, the heat from the semimolten polyethylene extruded around the shielding layer bonds the metal strip to the polyethylene jacket. If the heat imparted to the polyethylene material is sufficiently high, the aluminum tape will become hot enough so that bonding will also occur between overlapped layers of the shielding layer at the seam. The coated metallic tape firmly adheres to the outer jacket to further inhibit the penetration of moisture. The use of a shielding layer with a sealed seam also has been shown to have higher strength characteristics necessary to withstand repetitious bending of the cable.

Although the desired bond between the outer jacket and the core and the prevention of moisture penetration is solved by the use of a fully bonded sheath such as that described above, problems arise in terminating and splicing the cables. For example, it may be required that the polyethylene jacket be removed from the aluminum tape at a splice location or that a clamp be placed over the core and in contact with the inner surface of the metallic tape. An ear is formed at each end of the sheath clamp which protrudes through slots cut in the metallic tape and are exposed for engagement with a grounding clamp. Because of the intimate bond between the metallic tape and the jacket and between the metallic tape and the copolymer coating, it is difficult to bare the metallic tape to develop electrical contact at the splice location to assure that the shielding function of the aluminum tape takes place.

One alternative to the system which results in a fully bonded sheath is described in an application filed in the name of R. R. Wahlberg, Ser. No. 836,182, filed Apr. 1, 1969, now US. Pat. No. 3,574,016, to be granted Apr. 6, 1971. In that application, methods are disclosed for making a communications cable having a metallic strip surrounding a core and having at least one overlapped seam with an adhesive tape introduced into the seam to bond together the overlapping portions of the strip. That application also discloses (1) a partial coating of copolymer on the metallic strip so that when the strip is formed about the core, the copolymer is present only in the seam portion, (2) an adhesive copolymer film on only the inner major surface of the metallic strip and (3) combining a precoating of adhesive copolymer film on the inner major surface of the metallic strip with the introduction of a strip of adhesive material into the seam portion.

Of course, the cable could be manufactured with something less than an intimate bond between the jacket and the shield to facilitate splicing and grounding while still providing corrosion protection for the metal shielding tape. In at least one prior art patent, firm adhesion of the adhesive copolymer is restricted to only a portion of the interface between the jacket and the shielding layer. More specifically, the metallic tape is coated with a reactive carboxyl group material only along the longitudinal edge portions and for a limited predetermined distance on each side of the tape from the edges. The remainder of the tape is coated with a material having less adhesive qualities or may be coated with the same material over the entire width and then treated along a portion thereof intermediate the edges to reduce the adhesive characteristics of the coating in the portion intermediate the edges. (See U.S. Pat. No. 3,379,821 issued Apr. 23, 1968.)

However, any reduction in adhesive at the interface will be matched by a corresponding reduction in the absolute resistance to moisture penetration. In the cable construction just described, protection against moisture penetration depends upon a sealed seam. The absence of an intimate bond between the jacket and the shielding layer around the majority of the periphery of the cable presents the possibility of moisture penetration through pin holes with subsequent travel of the moisture along the length of the cable between the jacket and the shielding layer.

One solution to this problem is disclosed in US. Pat. No. 3,551,586, issued in the name of the applicants of this application on Dec. 29, 1970. There, a metallic tape having a release agent material applied selectively in at least one longitudinal strip on one major surface thereof is then coated over the strip and both major surfaces with an adhesive material. The tape is wrapped longitudinally about a cable core to form an overlapped seam which is then heated to bond the adhesive on the one major surface to the adhesive on the other major surface. The strip of release agent material may be easily removed together with the overlying adhesive to bare the metal to facilitate grounding at a splice location.

In many splicing operations, it is unnecessary to strip the outer jacket from the metallic shielding layer; and hence, the construction of the cable with reduced adhesive around a major. portion of the periphery unnecessarily increases the chance of moisture penetration. Moreover, even if it were necessary to strip the outer jacket from the metallic shielding layer in the splice location, it would seem incongruous to reduce the adhesion of the jacket to the shielding layer along the entire length of cable to expedite the stripping function for a short distance along the cable at the splices.

The type construction just described makes provi sions for splicing while simultaneously providing a reliably sealed adhesive-toadhesive seam at the overlap. In many types of cable seam constructions, the sealing of the overlap depends upon the development of an adhesive bond between an adhesive, say precoated on one of the overlapping metallic portions to the other uncoated metallic portion, or say the development of an adhesive bond of an adhesive tape to both metallic overlapping portions of the metallic shield.

It is therefore an'object of this invention to provide methods of manufacturing cables having a shielded metallic moisture barrier with an overlapped seam sealed with the requisite integrity by developing an adhesive bond between two adjacent contiguous adhesive materials at the overlapped seam and having portions of the shield bare for splicing purposes.

It is also an object of this invention to provide a cable having an outer jacket firmly bonded to a metallic shielding layer with a sealed longitudinal seam and having a bared inner surface of the metallic strip for splicing and grounding.

Of course, it is possible to merely coat one major surface of the aluminum strip with the adhesive copolymer. However, there would then be no adhesive on the other major surface to bond with the adhesive on the one major surface along the overlapped edge portions at the seam to form the desired sealed seam. In order to obtain a reliably sealed seam, the other major surface of the aluminum strip is preferably coated at least along the edge portion thereof with an adhesive material.

However, methods have not priorly been developed in which only a portion of one major surface is coated with adhesive copolymer material. This was due in part to the fact that if a plurality of strips of adhesive copolymer material were extruded on a web of aluminum, for example, and then wound on a take-up reel, the resulting roll, having an enlarged diameter altemating with voids across the transverse width of the roll because of the buildup of strips, would be exceedingly difficult to handle and slit. 7

Therefore, it is an object of this invention to provide cables and methods of making the cables in which one major surface of a metallic tape is precoated across the entire transverse width thereof with a first adhesive copolymer material and the other major surface has a stripe of a second adhesive material selectively applied on the tape to bond with the first adhesive material on the one major surface.

The term facing as employed in this specification and claims appended thereto when referring to the relationship between a surface and an object will be understood to mean that the surface is oriented in the direction of the object and may be, but is not necessarily, adjacent to or in contact with the object.

The term major surface as employed in this specification and appended claims when referring to surfaces of a strip of material or tape should be understood to include the large faces of the strip and not the edges of the strip even though the faces might have curved, corrugated or otherwise nonplanar configurations and even though the edges might blend smoothly into the faces without any sharp geometrical definition.

The term polymeric material as employed in this specification and appended claims will be understood to include both thermoplastic compounds such as polyethylene and polyvinyl chloride or the like, thermosetting compounds such as epoxies and polyurethanes and elastomers such as neoprenes.

SUMMARY OF THE INVENTION A cable illustrating certain features of the invention may include a core, and a metallic tape having inwardly and outwardly facing major surfaces, and surrounding the core with at least one overlapped seam formed between portions of the major surfaces of the tape with the radius of curvature of the tape being substantially equal to the radius of curvature of the core, the tape having an adhesive material precoated on at least part of an edge portion of one of the major surfaces of the tape forming the overlapped seam, further, the tape having an adhesive material precoated on the other major surface of the metallic tape along an edge portion thereof with 'the adhesive material on the other major surface being adhesively bonded to portions of the other facing major surface of the tape which forms the overlapped seam with a portion of the one major surface, the remaining portion of the other major surperature to seal the seam.

A method of manufacturing a cable and illustrating certain features of the invention may include the steps of advancing successive sections of a cable core along a predetermined path, applying successive portions of at least one metallic tape around successive sections of the cable core with at least one overlapped seam and such that the radius of curvature of the tape is substantially equal to the radius of curvature of the core, the tape having adhesive material precoated on at least part of an edge portion of one of the major surfaces of the tape forming the overlapping scam, the tape also having adhesive material precoated on at least part of the other major surface of the tape along an edge portion thereof with the adhesive material on the other major surface being at least adhesively bonded to the portion of the other major surface of the tape which forms the overlapped seam with a portion of the one major surface, the remaining portion of the other major surface of the tape being at least partially bare, the adhesive materials on the major surfaces capable of developing an adhesive bond along the overlapped seam at a predetermined temperature to seal the seam, and applying heat to successive portions of the overlapped seam to elevate'the temperature to the temperature at which the adhesive bond occurs.

Additional advantages and features of the. invention will be better comprehended by reference to the drawing and the detailed descriptions which follow.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of a cable taken transverse to a longitudinal axis of the cable which embodies the principles of the present invention with a metallic barrier, which includes a metallic tape, wrapped longitudinally about a core with an overlapped seam, to bond an adhesive material on an outwardly facing major surface of the tape to a stripe of adhesive material on an inwardly facing major-surface and having a jacket extruded thereover;

FIG. 2 is a cross-sectional view of the metallic tape taken transverse to a longitudinal axis of the tape and showing an adhesive material coated over the full transverse width of one major surface of the tape and a stripe of adhesive material on the other major surface adjacent a longitudinal edge thereof; 1

FIG. 3 is a view showing the cable at a splice location with a portion of the metallic barrier and jacket cut away from the core to permit insertion of a grounding ring at the splice location;

FIG. 4 is a sectional view of a cable taken transverse to the longitudinal axis of the cable manufactured in accordance with the principles of the method of this in- DETAILED DESCRIPTION Referring now to FIG. 1, there is shown a cable, designated generally by the numeral 10, and having a plurality of insulated conductors 11-11 comprising a core, designated generally by the numeral 12. The core 12 which is coextensive with the cable and which is enclosed by a core wrap (not shown) comprised of a paper tape or a rubber-polyethylene terephthalate laminate must be protected against moisture and corrosion.

Accordingly, to protect the core 12, a laminated shielding layer, or moisture barrier, designated generally by the numeral 13 (see FIG. 2), is wrapped longitudinally around the cable 10 to enclose the core (see FIG. 1). As is shown in FIG. 2, the moisture barrier 13 includes a metallic tape 14. The moisture barrier 13, prevents the diffusion of water vapor into the core 12 of the cable 10.

The metallic tape 14 of the moisture barrier 13 operates effectively to absorb the energy from stray electrostatic and electromagnetic fields emanating from sources outside the communications cable 10. It has been found that to best serve this purpose, the tape 14 is preferably made from an electrically continuous electrical conductor-grade aluminum alloy, approximately 0.008 inch thick. The particular metal and thickness of metal from which the metallic tape 14 is made is not important to this invention; if economic or technical considerations were to warrant it, the metal could be copper or brass or any of a number of other conductive materials.

The metallic tape 14 surrounds the core 12 with inwardly and outwardly facing major surfaces 16 and 17, respectively (see FIG. 2), of the tape in overlapped relation with each other along longitudinal edge portions thereof to form aseam 18 (see FIG. 1). The radius of curvature of the metallic tape 14 which surrounds the core 12 is substantially equal to the radius of curvature of the core. In the one type of cable construction shown in FIG. 1, which embodies the principles of this invention, the major surface 16 of the tape 14 faces inwardly toward the core 12, while the major surface 17 faces outwardly. In order to overcome the problems discussed hereinbefore, the longitudinal seam 18 must preferably be sealed while simultaneously making provisions for grounding the metallic tape 14 at splicing locations.

The major surfaces 16 and 17 of the aluminum tape 14 are selectively coated with adhesive materials at least along the portions thereof which form the overlapped seam, prior to assembly with the core 12, so that the adhesive on the inwardly facing major surface 16 bonds with the adhesive on the outwardly facing major surface 17 along the overlapped portions thereof while simultaneously providing a structure which exposes the inwardly facing major surface 16 of the shielding barrier 13 adjacent the cable core 12 for grounding connections (see FIG. 1). By developing a bond of adhesive material with adhesive material, a more reliably sealed seam 18 is obtained than by using methods which attempt to develop an adhesive-to-metal bond during the forming of the overlapped seam.

A stripe 19 of an adhesive copolymer material is applied longitudinally onto the inwardly facing major surface 16 of the aluminum tape 14 along a peripheral edge portion thereof (see FIG. 2). Additionally, an adhesive copolymer material is applied on the outwardly facing major surface 17 of the metallic tape 14 across the entire transverse width thereof to form a film 21 (see FIG. 2). In this way, theperipheral' edge portion of the adhesive film 21 on the outwardly facing major surface 17 is in engagement with and develops an adhesive bond with the stripe 19 on the peripheral edge portion of the inwardly facing major surface 16 of the tape 14 to seal the overlapping surfaces along the seam 18 (see FIG. 1).

The film 21 on the outwardly facing major surface 17 is an adhesive material which has the ability to develop firm adhesion to the metallic tape 14, and is highly resistant to corrosion and inhibits penetration of moisture into the cable core. Moreover, the adhesive material develops a firm bond with an overlying polyethylene jacket 22 (see FIG. 1), which is extruded over the moisture barrier 13. The adhesive materials which comprise the film 21 and the stripe 19 are selected so that when the metallic barrier 13 is wrapped around the core 12, the film and the stripe, under the application of heat, to raise the temperature to a predetermined temperature above ambient temperature, and pressure, are caused to develop a bond to seal the seam 18.

The materials of the stripe 19 and the film 21 on the inwardly and outwardly facing major surfaces 16 and 17, respectively, are comprised of ethylene acid copolymers. Although the materials of the stripe 19 and the film 21 may be adhesive copolymers having the same composition, the composition of the stripe is determined by the method used to form the stripe of a required thickness on the inwardly facing surface of the tape 14. For example, the film 21 is generally extruded over the outwardly facing major surface 17; if the stripe 19 could be extrusion-coated onto the major surface 17 the composition of the material in the stripe could be of the same composition as that in the film.

However, difficulties are encountered in attempting to extrude with a thin stripe of the desired dimension. In order to avoid the difficulties of slitting due to buildup on successive layers of a wound roll of moisture barrier 13, it may be desirous that the thickness of the stripe 19 is substantially less than the thickness of the film 21 on the moisture barrier 13.

Therefore, a copolymer solution may be used and the stripe 19 is painted, rolled or printed by conventional coating techniques on the major surface 17. 'Ac-. cordingly, the melt index and the acrylic acid content of the material of which the stripe 19 is comprised must be substantially greater than the melt index and the acrylic acid content of the material of which the film 21 is comprised. The acrylic acid content and the melt index of thecopolymer must be adjusted, e.g., -20 percent acrylic acid content, 100-200 melt index, so as to easily disperse the copolymer into solution.

Both the material for the stripe 19 and the material for the film 21 are available from commercial sources. For example, the film 21 may be composed of an ethylene acrylic acid copolymer such as that marketed by Dow Chemical Company of Midland, Mich. under the designation QX2375.0. Some examples of the copolymers for striping which are marketed are those of Union Carbide Company, under the designation EAA resin 9500, and by E. E. DuPont de Nemours and Company as Surlyn D dispersions.

Because of the properties of the QX2375 it is difficult to put the material into acqueous solution to get the required thickness of stripe. The QX2375 material has a melt index of approximately 5.0 and an acrylic acid content of 6-8 percent by weight. If the acrylic acid content were much higher, the adhesive would not bond to the jacket; if lower, the adhesive bonds better to the jacket, but then there is difficulty in bonding to the aluminum tape. The 6-8 percent acrylic acid content is therefore a compromise.

To achieve the thin stripe 19 required, e.g., one-third to one-half mil, the copolymer material-of the stripe must be tailored to easily disperse into solution. The BAA 9500 has a melt index of 150-200 and an acrylic acid content of 20 percent. The acrylic acid content is high to compensate for the higher melt index and hence the weaker polymer. The acrylic acid content serves as a hardening agent, and acts as a gripping agent as between the aluminum tape 14 and the resin to give the requisite bond strength. If the acrylic acid content were to be reduced, the bond strength between the aluminum and the adhesive or between the adhesive materials will be reduced accordingly.

The BAA resin 9500 and the SurlynD materials are both generic to salts of acrylic acid, the EAA 9500 being an ammonium salt, and the Suryln D being an alkaline metal salt. During the striping and curing process, the EAA 9500 is treated with ammonium to make an ammonia solution, the ammonia driven off from the EAA 9500 striping solution before driving off the water with an ethylene acrylic acid stripe 12 resulting which has properties different from those of the material of the film 21, e.g., the melt index and the acrylic acid content. But by using the Surlyn D dispersion, a salt is generated, as opposed to the acid of the EAA 9500, with the result that the stripe is composed of an acid and a complex salt. The Surlyn D may be treated with sodium hydroxide or zinc salt to make an alkali metal salt.

A solution of these copolymers may be effected by dispersing an acid copolymer in either an organic solvent or in water.

Generally, the stripe 19 is applied from a solution which is obtained by dispersing a high melt index ethylene acrylic acid copolymer of greater than 15 percent by weight acrylic acid in water which contains ammonium hydroxide. A salt of ethylene acrylic acid is formed which is coated onto the aluminum and dried.

Also, generally the material of the film 21 is selected so as to have a lower melting point than the material of the stripe 19. In this way, heat transfer takes place through the stripe 19 so that the film 21 contiguous with the stripe along the seam 18 melts and bonds to the stripe to seal the seam.

The physical size of the overlapping seam' 18 is an important factor in the ability of the moisture barrier 13 to prevent difiusion of water into the cable 10. The

rate at which water vapor diffuses through a material is proportional to the area which is exposed to the source of water vapor and the rate of diffusion is increasingly inversely proportional to the length of the path through which the water vapor must travel. It should be apparent that as the overlapped seam 18 of the moisture barrier 13 is increased in width and as the thickness of the adhesive seal in the seam decreases, the ability of the adhesive seal to prevent moisture diffusion is in-- creased. As a practical matter, it becomes necessary to assign definite dimensions to the seal. Cost and manufacturing considerations are factors which have led to a determination of optimum dimensions for the adhesive seal.

By applying a stripe 19 of adhesive material along an edge portion of the aluminum tape 14 along the inwardly facing major surface 16 thereof, and then coating the entire outwardly facing major surface 17 with the adhesive copolymer film 21, the mating major surfaces 16 and 17, alongthe overlapped edges, form the sealed seam 18 and a moisture resistant tubular shield is formed around the cable core 12. The resistance of the cable 10 against the penetration of moisture is further improved by applying the polyethylene jacket 22 to the outwardly facing major surface of the adhesive copolymer film 21 under extruding temperatures which are designed to yield optimum bonding of the polyethylene to the barrier 13.

Moreover, the sealed seam 18 along the overlapping edges of the moisture barrier 13 produces a cable having improved strength characteristics which gives prolonged useful like although subjected to repeated bendmg.

The construction of the cable 10in accordance with the principles of this invention gives a reliably sealed seam 18. During the forming of the temperature barrier 13 to surround the core 12, various lubricants are used in the equipment. If one of the major surfaces were bare, the lubricants may contaminate the surface of the portion thereof that bonds with an adjacent contiguous portion of the other major surface. This contamination detracts from the development of a reliable adhesive bond between the adhesive on the one major surface to the bared other surface. By using a stripe 19 so as to obtain an adhesive-to-adhesive bond, as opposed to adhesive-to-metal, at the overlap, this problem is overcome. Moreover, at line speeds now in use, it is difficult to obtain a reliably sealed adhesive-to-metal seam.

The construction of the cable 10in accordance with this invention also facilitates the grounding of the cable at a splice location. For example, during installation and at a splicing location, the jacket 22 and metallic barrier 13 may be slit and pulled away from the core 12 as shown in FIG. 3. Then an installer inserts a grounding ring 23 having cars 24 under and in electrical engagement with the bared portion of the inwardly facing major surface 16 of the tape 14.

Other types of cable construction which embody the principles of this invention, may require that the outwardly facing major surface 17 of the metallic barrier 13 be barred for grounding at splice locations. Referring now to FIG. 4, the core 12 of another type of cable construction includes conductors 11 and an inner polyethylene jacket which encloses the conductors. The adhesive copolymer film 21 is coated across the entire width of the inwardly facing major surface 16 with the stripe 19 applied along one longitudinal edge of the outwardly facing major surface 17. In this way, the major surface 16 is bonded intimately to the core 12'while the jacket 22 is extruded over and in direct contact with the major surface 17.

METHOD OF MAKING In the method of making a cable which embodies the principles of the present invention, aluminum sheet stock may have a film 21 of ethylene acrylic acid copolymer precoated across one major surface 17 thereof. The adhesive material in the film 21 has the ability to develop an adhesive bond at a predetermined temperature above ambient temperature. The precoated aluminum is taken up in a roll (not shown) and slit into tape-size widths, each of the tapes 14 having one major surface 17-precoated with a film 21 of ethylene acrylic acid polymer.

An aluminum tape 14 precoated across the entire width of one major surface 17 thereof, with a first adhejacket 22 is caused to 652%}; an adhesive bond with the jacket to achieve a fully bonded sheath.

After the polyethylene jacket 22 has been extruded over the core 12 and moisture barrier 13, provisions must be made to prevent an excessive amount of heat flowing from the hot plastic jacketing material inwardly toward the core. This sometimes damaging heat flow is accomplished by rapidly chilling the plastic jacket 22,

sive copolymer material, is available commercially such as, for example, from the Dow Chemical Company under the designation Zetabond. A stripe 19 of a second adhesive ethylene acrylic acid copolymer is applied from a solution and precoated along a longitudinal edge portion of the other major surface 16 thereof which is to form the overlapped seam 18 with a portion of the outwardly facing major surface. Then successive portions of the tape 14 are advanced in registration with successive sections of the core 12 into a tube forming device, designated generally by the numeral 26 (see FIG. 5).

Referring not to FIG 5, the metallic tape 14 is wrapped longitudinally about the advancing successive sections of the core 12 by the tube forming device 26 to enclose the core and to form the overlapping seam 18 between the inwardly facing major surface 16 of the strip and the outwardly facing major surface 17 thereof. As can be seen in FIG. 1, the tape 14 is wrapped about the core 12 so that the radius of curvature of the tape is substantially equal to the radius of curvature of the core. Then the enclosed core 12 is advanced to, and through, a conventional plastic extruder, designated generally by the numeral 27, which is used to extrude the circumferential jacket 22 of polyethylene over the metallic tape 14 of the barrier 13. This raises the temperature to the predetermined temperature and causes an adhesive bond to be developed between the adhesive materials on the overlapping portions of the opposite surfaces of the tape.

Molten polyethylene may be fed from the extruder 27 at a temperature of from 375 to 475F. It is more desirable to restrict the temperature range to one of 25F between 425F and 450F. There is sufiicient heat within the polyethylene so that the heat transfer takes place through the copolymer film 21 contiguous the jacket 22 through the metallic tape 14 and the strip 19 to melt the portion of the film in the seam 18 to bond to the stripe. Simultaneously, the film 21 contiguous the with any of several apparatus (not shown) well known in the art.

Alternately,.the overlapped bonded seam 18 may be formed independently of the extrusion of the jacket 22. Successive portions of the metallic tape 14, precoated with the stripe 19 and film 21 on the major surfaces 16 and 17, respectively, are drawn into an induction-heating unit (not shown) similar to those units disclosed in U.S. Pat. Nos. 2,758,189, 2,801,316 and 2,925,485 which issued on Aug. 7, 1956, July 30, 1957 and Feb. 16, 1960, respectively, to D. A. Hughes. Other types of apparatus which employ flame heating or hot air may be used to apply heat to successive portions of the seam As the metal covered core unit 12 is passed through the induction-heating unit (not shown), high frequency magnetic fields develop currents within the seam portion of the moisture barrier 13, to heat the seam. By properly controlling the power with conventional control means (not shown), sufficient heating may be provided to accomplish bonding in the seam portion without degradation of the copolymer or damage to the core 12. A water-quenching station (not shown) may be located immediatelyadjacent the exit end of the induction-heating unit (not shown) to spray water at ambient temperature onto the seam portion to cool the seam while maintaining pressure therein. Any moisture on the barrier 13 is removed to prepare the now enclosed core 12 for a jacketing operation.

After the metallic tape 14 is formed into a tubular shape on the core unit 12 with a bonded overlapped seam 18, the subassembled cable unit may be taken up on a reel (not shown) and the polyethylene jacket 22 applied to the outwardly facing major surface of the copolymer film 21. One of the advantages in using the two step operation of heating and later jacketing is that the integrity of the sealed seam 18 can be checked before the polyethylene jacket 22 is applied. Various techniques can be used to check the integrity of the ad hesive seal. One technique is described in U.S. Pat. No. 2,988,917 issued on June 20, 1961 to C. A. Hallam et al.

The use of a forming, sealing and seam integrity checking system, independent of a jacket extrusion operation, allows for starts and stops to make repairs without impairing the extrusion operation. If circumstances were to make it unimportant to be able to start and stop the forming and sealing operation, the application of the jacket 22 could be accomplished in a tandem operation without intermediate reeling of the core unit 12. A conventional device (not shown) for checking the integrity of the adhesive seal could be used in a scheme wherein faulty areas were marked so that they could be repaired or cut out of the cable 10 after the jacket 22 has been applied.

The cable 10 may also be assembled, employing the principles of the method of this invention, to provide for grounding the outwardly facing (see FIG. 4 major surface 17 of the metallic tape 14. Accordingly, the precoated tape 14, is wrapped about the core 12 to overlap the stripe 19 along a longitudinal peripheral edge portion of the outwardly facing major surface 17 of the tape with the copolymer film 21 on the inwardly facing major surface 16. Then the jacket 22 is extruded over the barrier 13 in intimate contact with the exposed outwardly facing surface 17 of the tape 14.

In one example of a cable manufactured in accordance with the principles of this invention,-a.n aluminum tape 14 having a width of from 8% to 8% inches and a thickness of from 6 to 8 mils is precoated with an ethylene acrylic acid copolymer to form a film 21 which has a thickness of approximately 2 mils. Then the precoated tape 14 is coated with a solution of adhesive copolymer having a high acrylic acid content to form a stripe 19 on the major surface 16 of the tape. The stripe 19 has a thickness of one-third to one-half mil and has a width of 1 inch. The barrier 13 including the tape 14 having the stripe 19 and film 21 therein was wrapped longitudinally about an advancing core having a diameter of 2.45 inches. Then a polyethylene jacket 22 was extruded over the shielded core to complete the cable 10.

It would be within the scope of this invention to form a tubular member from a metallic tape by wrapping successive portions of the tape into a tubular shape having an overlapped seam such that no portions of the tape are retroflexed. The tape is precoated with an adhesive material on at least part of an edge portion of one of the major surfaces of the tape facing the overlapped seam, and precoated with an adhesive material on at least part of the other major surface which forms the overlapped seam with the one major surface such that the adhesive materials are caused to develop a bond along the overlapped seam. The remaining portion of the other major surface of the tape is at least partially bare.

The tape from which the tubular member is formed could have an adhesive material applied over the entire transverse width of the outwardly facing surface. Of course, in that instance, the adhesive material on the outwardly facing major surface could conceivably act as an insulating barrier to the transfer of heat to the abutting adhesive materials along the overlapped seam. In order to transfer the necessary heat through this potential insulating barrier and achieve a suitable bond along the overlapping seam, it may be necessary to provide an excessive amount of heat or allow the heat transfer to take place over a longer period of time. This latter course of action can only be achieved by decreasing the linear rate at which the elongated member moves through the manufacturing process. A decrease in the cable feeding or cooling rate'causes a decrease in production output or increase in floor space required with accompanying increase in cost of the manufactured product.

Should there be problems in heat transfer to the seam, it would be within the scope of the invention to omit the adhesive material on the outwardly facing major surface, for example, along an edge portion thereof opposite the overlapped seam. Then heat could be applied directly to uncoated successive portions of the metallic tape.

It is to be understood that the term tubular membet as used in the specification andclaims includes not only a cable having a core, but a tape formed into a tubular shape without a core as well as a single conductor having insulation applied thereover.

It is to be understood that the above-described embodiments are simply illustrative of the invention and that many other embodiments can be devised without departing from the scope and spirit of the invention.

What is claimed is:

1. An electrical cable, comprising a core; and

a metallic tape having inwardly and outwardly facing major surfaces, and surrounding the core with at least one overlapped seam formed between portions of the major surfaces of the tape with the radius of curvature of the tape being substantially equal to the radius of curvature of the core;

the tape having a first adhesive material precoated on at least part of an edge portion of one of the major surfaces of the tape forming the overlapped seam; further, the tape having a second adhesive material precoated on the other major surface of the metallic tape along an edge portion thereof with the ad-- hesive material on the other major surface being adhesively bonded to portions of the other major surface of the tape which forms the overlapped seam with a portion of the one major surface, the remaining portion of the other major surface of the tape being at least partially bare; an adhesive bond occurring between the first and the second adhesive materials precoated on .the portions of the major surfaces forming the overlapped seam;

the adhesive materials on the major surfaces being capable of developing an adhesive .bond at a predetermined temperature along the overlapped seam; I

the first and the second adhesive materials composed essentially of ethylene acrylic acid copolymers;

the second adhesive copolymer material having a melt index and an acrylic acid content which are substantially greater than the melt index and the acrylic acid content, respectively, of the first adhesive material.

2. An electrical cable, comprising:

a core; and

a metallic tape having inwardly and outwardly facing major surfaces, and surrounding the core with at least one overlapped seam formed between portions of the major surfaces of the tape with the radius of curvature of the tape being substantially equal to the radius of curvature of the core;

the tape having a first adhesive material precoated on one of the major surfaces of the tape across the entire transverse width thereof;

further, the tape having a second adhesive material precoated on the other major surface of the metallic tape along an edge portion thereof and being substantially restricted in location to and adhesively bonded to portions of the other major surface of the tape which forms the overlapped seam with a portion of the one major surface, the remaining portion of the other major surface of the tape being bare;

an adhesive bond occurring between the first and the second adhesive materials precoated on the portions of the major surfaces forming the overlapped seam; g

the adhesive materials on the major surfaces being capable of developing an adhesive bond at a predetermined temperature along the overlapped scam;

the first and the second adhesive materials being composed essentially of ethylene acrylic acid copolymers;

the second adhesive copolymer material having a melt index and an acrylic acid content which are substantially greater than the melt index and the acrylic acid content, respectively, of the first adhesive material. I

3. The cable of claim 2, wherein the thickness of the precoating of first adhesive material is substantially greater in thickness than the precoating of second adhesive material.

4. The cable as set forth in claim 2, wherein the second adhesive material is capable of being applied in the form of a solution to the metallic tape.

5. The cable of claim 4, wherein the copolymer solution is a high melt index ethylene acrylic acid copolymer of greater than 15 per cent by weight acrylic acid in water solution which contains ammonium hydroxide.

6. An electrical cable, comprising:

a core;

a metallic tape having inwardly and outwardly facing major surfaces, the metallic tape surrounding the core and having an overlapped seam with the radius of curvature of the tape being substantially equal to the radius .of curvature of the core;

an extruded jacket of polymeric material surrounding the core and the metallic tape;

a first adhesive material precoated on the outwardly facing major surface of the metallic tape across the entire transverse width thereof;

a second adhesive material precoated on the inwardly facing major surface of the metallic tape along an edge portion thereof and being substan-- tially restricted in location to and adhesively bonded to portions of the inwardly facing major surface of the tape which forms the overlapped seam with a portion of the outwardly facing major surface, the remaining portion of the inwardly facing major surface of the tape being bare; and

an adhesive bond existing between the contiguous adjacent first and second adhesive materials along the overlapping scam;

the adhesive materials on the major surfaces capable of developing a bond at a predetermined temperature less than the temperature at which the jacket is extruded;

the first and the second adhesive materials being composed essentially of ethylene acrylic acid copolymers;

the second adhesive copolymer material having a melt index and an acrylic acid content which are substantially greater than the melt index and the acrylic acid content, respectively, of the first adhesive material.

7 The cable of claim 6, wherein:

the first adhesive material is bonded to the second adhesive material along the overlapped seam, the first adhesive maten bonded to t e acket; and

the first adhesive material is capable of bonding to the second adhesive material at the predetermined temperature which is less than the temperature at which the jacket is extruded, the second adhesive material having a melting point which is higher than the predetermined temperature. 

1. An electrical cable, comprising a core; and a metallic tape having inwardly and outwardly facing major surfaces, and surrounding the core with at least one overlapped seam formed between portions of the major surfaces of the tape with the radius of curvature of the tape being substantially equal to the radius of curvature of the core; the tape having a first adhesive material precoated on at least part of an edge portion of one of the major surfaces of the tape forming the overlapped seam; further, the tape having a second adhesive material precoated on the other major surface of the metallic tape along an edge portion thereof with the adhesive material on the other major surface being adhesively bonded to portions of the other major surface of the tape which forms the overlapped seam with a portion of the one major surface, the remaining portion of the other major surface of the tape being at least partially bare; an adhesive bond occurring between the fIrst and the second adhesive materials precoated on the portions of the major surfaces forming the overlapped seam; the adhesive materials on the major surfaces being capable of developing an adhesive bond at a predetermined temperature along the overlapped seam; the first and the second adhesive materials composed essentially of ethylene acrylic acid copolymers; the second adhesive copolymer material having a melt index and an acrylic acid content which are substantially greater than the melt index and the acrylic acid content, respectively, of the first adhesive material.
 2. An electrical cable, comprising: a core; and a metallic tape having inwardly and outwardly facing major surfaces, and surrounding the core with at least one overlapped seam formed between portions of the major surfaces of the tape with the radius of curvature of the tape being substantially equal to the radius of curvature of the core; the tape having a first adhesive material precoated on one of the major surfaces of the tape across the entire transverse width thereof; further, the tape having a second adhesive material precoated on the other major surface of the metallic tape along an edge portion thereof and being substantially restricted in location to and adhesively bonded to portions of the other major surface of the tape which forms the overlapped seam with a portion of the one major surface, the remaining portion of the other major surface of the tape being bare; an adhesive bond occurring between the first and the second adhesive materials precoated on the portions of the major surfaces forming the overlapped seam; the adhesive materials on the major surfaces being capable of developing an adhesive bond at a predetermined temperature along the overlapped seam; the first and the second adhesive materials being composed essentially of ethylene acrylic acid copolymers; the second adhesive copolymer material having a melt index and an acrylic acid content which are substantially greater than the melt index and the acrylic acid content, respectively, of the first adhesive material.
 3. The cable of claim 2, wherein the thickness of the precoating of first adhesive material is substantially greater in thickness than the precoating of second adhesive material.
 4. The cable as set forth in claim 2, wherein the second adhesive material is capable of being applied in the form of a solution to the metallic tape.
 5. The cable of claim 4, wherein the copolymer solution is a high melt index ethylene acrylic acid copolymer of greater than 15 per cent by weight acrylic acid in water solution which contains ammonium hydroxide.
 6. An electrical cable, comprising: a core; a metallic tape having inwardly and outwardly facing major surfaces, the metallic tape surrounding the core and having an overlapped seam with the radius of curvature of the tape being substantially equal to the radius of curvature of the core; an extruded jacket of polymeric material surrounding the core and the metallic tape; a first adhesive material precoated on the outwardly facing major surface of the metallic tape across the entire transverse width thereof; a second adhesive material precoated on the inwardly facing major surface of the metallic tape along an edge portion thereof and being substantially restricted in location to and adhesively bonded to portions of the inwardly facing major surface of the tape which forms the overlapped seam with a portion of the outwardly facing major surface, the remaining portion of the inwardly facing major surface of the tape being bare; and an adhesive bond existing between the contiguous adjacent first and second adhesive materials along the overlapping seam; the adhesive materials on the major surfaces capable of developing a bond at a predetermined temperature less than the temperature at which the jacket is extruded; the first and the second adhesive materials being composed essenTially of ethylene acrylic acid copolymers; the second adhesive copolymer material having a melt index and an acrylic acid content which are substantially greater than the melt index and the acrylic acid content, respectively, of the first adhesive material. 